İrem Bakır | Searcharxiv

arXiv2026

On the origin of the strong internal magnetic fields of central compact objects

Central compact objects are radio-quite young neutron stars associated with supernova remnants. They have relatively small dipole fields, $B_{\rm p} \sim 10^{10}\,{\rm G}$ as inferred from their spin parameters. X-ray observations and theoretical arguments imply the presence of stronger internal magnetic fields. We argue that the dipole fields of these objects are very close to what they had inherited from the \textit{core} of the progenitor by flux conservation and their small initial rotation frequency does not allow for the $α$-process to enhance their poloidal fields. Although a full-fledged dynamo process can not proceed, relatively strong toroidal magnetic fields, $B_ϕ\sim 10^{13}\,{\rm G}$, can be generated from the seed poloidal fields via the $Ω$-effect in the proto-neutron star stage. We present a simplistic model for these processes and further speculate that the reason why these objects are born relatively slow-rotating is that they were not spun-up by acquiring angular momentum from the fallback matter.

astro-ph.HE↗

arXiv2026

Evolution of proto-neutron stars to pulsars, magnetars and central compact objects

Some young neutron stars, the magnetars, have ultra-strong magnetic fields, yet their inferred birth rate is comparable to the core-collapse supernova rate, challenging scenarios that require rare, extreme conditions. We propose that this discrepancy can be reconciled if both pulsars and magnetars pass through a dynamo process during the proto-neutron star (PNS) phase. We employ a shear-driven $α$--$Ω$ dynamo model that includes PNS contraction. The dynamo generically produces toroidal-dominated fields set mainly by the $Ω$-effect. The evolution of the poloidal field is first dominated by flux conservation during collapse and then by the $α$-effect. The saturated toroidal field depends strongly on the initial value of the shear, with a threshold at $q_0 \simeq 0.23$; below this, the poloidal field remains near the value obtained by the flux-conservation ($\approx 2.5\times10^{10}\,{\rm G}$). For the shortest initial periods, the model leads to magnetar-like strengths ($B_{\rm p} \simeq 10^{15}\,{\rm G}$, $B_ϕ\simeq 10^{16}\,{\rm G}$), while for the slower rotators it yields ordinary pulsar fields ($B_{\rm p} \simeq 10^{12}\,{\rm G}$, $B_ϕ\simeq 10^{14}\,{\rm G}$). We also argue that the central compact objects can acquire toroidal fields amplified solely by the $Ω$-effect; lacking the $α$-effect, their poloidal fields are not shaped by the dynamo effect.

astro-ph.HE↗